Esters have been used as lubricating oils for over 50 years. They are used in a variety of applications ranging from jet engines to refrigeration. In fact, esters were the first synthetic crankcase motor oils in automotive applications. However, esters gave way to polyalphaolefins (PAOs) due to the lower cost of PAOs and their formulation similarities to mineral oils. In full synthetic motor oils, however, esters are almost always used in combination with PAOs to balance the effect on seals, additives solubility, volatility reduction, and energy efficiency improvement by enhanced lubricity.
Ester-based lubricants, in general, have excellent lubrication properties due to the polarity of the ester molecules of which they are comprised. The polar ester groups of such molecules adhere to positively-charged metal surfaces creating protective films which slow down the wear and tear of the metal surfaces. Such lubricants are less volatile than the traditional lubricants and tend to have much higher flash points and much lower vapor pressures. Ester-based lubricants are excellent solvents and dispersants, and can readily solvate and disperse the degradation by-products of oils. Therefore, they greatly reduce sludge buildup. While ester-based lubricants are stable to thermal and oxidative processes, the ester functionalities give microbes a handle to do their biodegrading more efficiently and more effectively than their mineral oil-based analogues. However, the preparation of esters is more involved and more costly than the preparation of their PAO counterparts.
Triester-based lubricants and their manufacture have been recently reported, wherein the triester species have a general formula:
where R1-4 are the same or independently selected from C2 to C20 hydrocarbon groups, and n is an integer from 2 to 20. See commonly-assigned U.S. patent application Ser. No. 12/122,894; filed Apr. 4, 2007 and published as United States Patent Publication No. 20080248982. Note that the ester group comprising R2 is attached to the aliphatic backbone via an inverted (non-homologous) linkage (compared to the ester groups comprising R3 and R4).
In view of the foregoing, and not withstanding such above-described advances in triester-based lubricant synthesis, facile methods of generating triester-based lubricants would be extremely useful—particularly wherein the triester species in said lubricants comprise homologous linkages between all three ester groups and the aliphatic backbone.